Recently, a new class of materials known as geopolymers has emerged in cement concrete products. Geopolymers are not only considered to be a potential alternative to standard cement, but they also present an opportunity to convert a variety of industrial wastes into interesting by-products. Because geopolymers can exhibit good mechanical strength and resistance in front of alterations by aggressive environments, they are currently attracting great interest for their potential use in simultaneously improving both environmental and engineering performance compared with traditional technologies. Geopolymers are conventionally formed by polymerisation of aluminosilicate oxides in the presence of a strongly basic activating agent. According to the state of the art, the polymerisation is initiated by a liquid alkaline silicate. This is generally favoured by the reaction mechanisms as described in the scientific literature: In accordance with Fernández-Jiménez A. et al. (Cement and Concrete Research, 35 (6), pages 1204 to 1209, 2005), a dissolution of a solid aluminosilicate by alkaline hydrolysis is the first reaction step and leads to the formation of aluminates and silicates. Once a formation equilibrium is obtained, a saturated solution is formed which leads to a network of oligomers that undergo polycondensation to form a three-dimensional network of aluminosilicates. This process requires a very large amount of water that subsequently is partially removed from the product.
Recently, some research has been focussed on providing precursors for forming geopolymers that may be easily stored, handled and transported, in order to obtain the finished product on sites where it is required. Ideally, the finished product may be obtained by simply adding water to a precursor and forming a geopolymer that way.
US 2011/0132230 A1 (Han et al.) discloses dry mixtures as geopolymeric precursors, comprising a water soluble metal silicate powder and aluminosilicate powder. The geopolymeric precursors may further comprise supplemental ingredients, such as for example, but not necessarily, a particulate solid alkali base. These dry mixtures require a high amount of water to be added in order to produce a geopolymer product. Furthermore, the aluminosilicate present requires a high content of amorphous phase, such as 90 wt.-% or greater.
It is an object of the present invention to provide a dry mixture having a low water demand for forming geopolymers with the desired mechanical properties.
It is a further object of the present invention is to provide a process for preparing a geopolymer on site by just adding water.